[Factors related to occurrence of twin pregnancy after double-embryo transfer in vitro fertilization cycles].

Objective: To analysis high risk factors of twin pregnancy after double-embryo transfer in fresh in vitro fertilization-embryo transfer (IVF-ET) cycles.

Methods: From Jan. 2003 to Dec. 2007, 275 infertile cases underwent IVF-ET or intracytoplasmatic sperm injection (ICSI) and obtained clinical pregnancy in Reproductive Medical Center, Ruijin Hospital affiliated to Shanghai Jiaotong University. A total of 280 cycles were performed, which were classified into single pregnancy group (198 cycles) and twin pregnancy group (82 cycles). The general information, patient and embryo characteristics were compared between those two groups, then univariate and multivariate regression were analyzed.

Results: (1) There was no statistical difference in the following clinical features between single and twin pregnancy groups, such as patients ages, the ratio of secondary infertility, period and possible causes of infertility (P > 0.05). (2) When comparing basal level of follicle stimulating hormone (FSH), mean numbers of follicles, mean obtained ovum, ovarian responsibility (ratio of follicle stimulation hormone dose/number of oocyte retrieved), endometrial thickness given by human chorionic gonadotropin (hCG), no significant difference were observed between two groups (P > 0.05). Twin pregnant group had fewer cycles of in vitro fertilization treatment when compared with single pregnancy group (0.18 +/- 0.16 vs. 0.22 +/- 0.21, P = 0.03). (3) No significant difference was observed in the following clinical index, including fertilization approaches, mean numbers of embryo, mean score of transferred embryo, developmental stage of top quality embryo, morphological score of embryo, morphological score of the second best embryo transferred (P > 0.05). The number of top-quality embryos and the development stage score of the second best embryo transferred were higher than those of single pregnant group (3.8 +/- 3.3 vs. 2.9 +/- 2.5, P < 0.05 and 3.7 +/- 0.2 vs. 3.4 +/- 0.2, P < 0.05). (4) Multivariate regression analysis showed that four variables was correlated independently with twin pregnancy including first treatment cycle of IVF-ET (OR = 1.82, P = 0.02), number of good quality embryos (OR = 1.35, P = 0.01), development stage score of the second best embryo (OR = 1.55, P = 0.009) and ovarian responsibility (OR = 0.96, P = 0.04).

Conclusions: It is advisable to perform single embryo transfer. If patients are at high risk factors of twin pregnancy including initial IVF-ET treatment, good ovarian responsibility, more number of top-quality embryos and development stage score of the second best embryo transferred.